PHP dynamic file inclusion problems

The index. PHP content is as follows: PHPcode & lt ;? Phpfunctiona1 () {require_once_t.php;} b1 (); _ t. php file content: PHPcode & lt ;? Phpfunctionb1 () {echo & quot; dddddddd & quot ;}
The content of index. php is as follows:

PHP code

The content of the _ t. php file is as follows:

PHP code

In this way, an error will be reported. if you cannot find the b1 () function, how can we achieve this dynamic inclusion of a file? This file is a function extension library and can be used globally.

In the CodeIgniter framework, the Loader class dynamically loads libraries and class files. Why can it work?

------ Solution --------------------
B1 (); before, there must be a1 ();

------ Solution --------------------
.....
Of course you cannot find that you have not run a1 ();